Ecuatii si inecuatii de gradul al doilea si reductibile la gradul al ...
Ecuatii si inecuatii de gradul al doilea si reductibile la gradul al ...
Ecuatii si inecuatii de gradul al doilea si reductibile la gradul al ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Ecuatia <strong>de</strong> <strong>gradul</strong> <strong>al</strong> <strong>doilea</strong> cu a = 1 se numeste ecuatie patrata redusa <strong>si</strong> se noteaza <strong>de</strong><br />
regu<strong>la</strong><br />
x 2 + px + q = 0 (4)<br />
<strong>si</strong> formulele (2) <strong>si</strong> (3) <strong>de</strong> c<strong>al</strong>cul <strong>al</strong>e radacinilor <strong>de</strong>vin<br />
<strong>Ecuatii</strong>le <strong>de</strong> forma<br />
x1,2 = − p<br />
2 ±<br />
<br />
p 2 − q, (∆ > 0) (5)<br />
2<br />
x1 = x2 = − p<br />
, (∆ = 0). (6)<br />
2<br />
ax 2 + bx = 0, (7)<br />
ax 2 + c = 0. (8)<br />
se numesc ecuatii <strong>de</strong> <strong>gradul</strong> <strong>al</strong> <strong>doilea</strong> incomplete. <strong>Ecuatii</strong>le (7), (8) pot fi rezolvate cu ajutorul<br />
afirmatiei 1 sau <strong>al</strong>tfel, mai <strong>si</strong>mplu:<br />
ax 2 + bx = 0 ⇔ x(ax + b) = 0 ⇔<br />
ax 2 + c = 0 ⇔ x 2 = − c<br />
a ⇔<br />
Exemplul 2. Sa se rezolve ecuatiile<br />
⎡<br />
⎣ x1 = 0;<br />
x2 = − b<br />
a .<br />
⎡ ⎧ <br />
⎪⎨<br />
⎢ x1,2 = ± −<br />
⎢<br />
⎪⎩<br />
⎢<br />
⎣<br />
c<br />
a ,<br />
ac ≤ 0,<br />
<br />
x ∈ ∅,<br />
ac > 0.<br />
a) 2x 2 − 7x = 0; b) 9x 2 − 25 = 0; c) √ 2x 2 + 3 = 0.<br />
Rezolvare. a) 2x 2 − 7x = 0 ⇔ x(2x − 7) = 0 ⇔<br />
⎡<br />
⎢<br />
⎣<br />
x1 = 0,<br />
x2 = 7<br />
2 ;<br />
b) 9x 2 − 25 = 0 ⇔ 9x 2 = 25 ⇔ x 2 = 25<br />
9 ⇔ x1,2 = ± 5<br />
3 ;<br />
c) √ 2x 2 + 3 = 0 ⇔ x 2 = − 3 √ 2 , <strong>de</strong> un<strong>de</strong> rezulta ca ecuatia nu are radacini (membrul din<br />
stanga eg<strong>al</strong>itatii este nenegativ, iar cel din dreapta - negativ).<br />
In continuare vom an<strong>al</strong>iza cateva exemple <strong>de</strong> ecuatii ce se reduc <strong>la</strong> rezolvarea ecuatiilor <strong>de</strong><br />
<strong>gradul</strong> <strong>al</strong> <strong>doilea</strong>.<br />
0 Copyright c○1999 ONG TCV Sco<strong>al</strong>a Virtu<strong>al</strong>a a Tanarului Matematician http://math.ournet.md<br />
2